A Buffalo museum has made a rare discovery within its own collection: a fully intact egg from the extinct elephant bird that until now, was thought to be fake.

Curators at the Buffalo Museum of Science were cataloging pieces in the museum’s collection when they realized and confirmed that the foot-tall egg had been mislabeled as a model. Measuring 28 inches around, it weighs more than 3 pounds.

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Experts said there are fewer than 40 intact elephant bird eggs held in public institutions.

The flightless elephant bird was native to Madagascar. It grew to be 10 feet tall, weighed between 770 and 1,100 pounds and laid the largest eggs of any vertebrate, including dinosaurs.